Sub Station Seven was one of seven buildings that provided power to the elevated trains operated by the Manhattan Railway Company on Second, Third, Sixth and Ninth Avenues. These substations received 11,000-volt alternating current from the power house at 74th Street and the East River and converted it to 625-volt direct current for the third-rail distribution system to the trains. The power station and substations began operating in late 1901, and all trains were running by electric power by the spring of 1903.

No. 7 was the primary supply of power for the upper portion of the Lexington Avenue subway from 1918 into at least the late 1970s, when other substations were constructed underground. It is the only Manhattan substation that dates from the electrification of the pre-subway elevated system and also retains its original appearance.